1. Field of the Invention
This invention relates to a tensioning system for a drive belt passing around at least two pulleys.
2. Description of the Prior Art
It is well known to transmit drive from a motor or other live shaft to a further rotatable shaft by means of a belt and pulley system. The peripheries of the pulleys may be smooth, and in this case the inner side of the belt will also normally be smooth. However, when it is required that the driving and driven shafts should be synchronized, the peripheries of the pulleys may be toothed and in this case the inner surface of the belt will also be toothed to correspond.
The driving shaft may be used to transmit torque to a single driven shaft or it may be used to drive two or more shafts. In the latter case each driven shaft will be provided with a pulley and the belt will pass around all of the pulleys.
It is also well known that a belt drive system can only operate satisfactorily if the tension in the belt is maintained within certain limits. Thus, for example, if the belt is too tight, there will be unacceptable wear on the bearings of the various shafts, whereas, if the belt is too slack, slippage may occur between the driving and driven shaft or shafts. In an extreme case, if the belt is too slack, it may even become disengaged from one or more of the pulleys.
In order to maintain the required tension in the belt, the piece of apparatus supporting the bearing for one or more of the shafts may be mounted in such a way that the respective shaft may be moved towards, or away from, the other shaft or shafts. Where such an adjustable mounting is not practicable, an idler device comprising an idler pulley or idler bearing surface may be provided in the path of the belt between two of the pulleys.
Such an idler device will be adjustable in a direction normally at right angles to the undeflected path of the belt so that the total distance of the belt travel may be increased or decreased by movement of the idler device. If both surfaces of the belt are smooth, the idler device may be arranged to deflect the belt either inwardly or outwardly. However, when a toothed belt is used, it will normally be desirable to mount the idler device in such a way that it contacts the outer surface of the belt and may be used to deflect the belt inwardly. As already mentioned, the belt tension, when the belt and pulleys are stationary, must be adjusted accurately. For this purpose it is usual to make use of a force gauge during adjustment of the tensioning device. In a complicated piece of machinery it may be difficult to use a force gauge during the adjustment process and in many cases, even if it is practicable to use the force gauge under initial assembly conditions in a factory, it may not be practicable to use the gauge when adjustments are required outside the factory.